Slide 1 of 15
Marijuana has a reputation as a relatively harmless drug, but researchers are learning more and more about the effects it may have on the brain.
An increased risk of psychosis, changes in the brain's reward system and the scrambled neuron signals that may underlie "the munchies" are just some of the many potential effects of marijuana use on the brain.
"The biggest risk related to the use of marijuana is the increased risk of psychosis," said Dr. Scott Krakower, assistant unit chief of psychiatry at Zucker Hillside Hospital in Glen Oaks, New York. Another significant risk, for those who use marijuana during their teenage years, is an increased likelihood of an IQ drop.
"It is safe enough to say that people who smoke marijuana," especially when they are young, are more likely have a reduction in their IQ later in life, Krakower told Live Science. [11 Odd Facts About Marijuana]
Here's a look at the recent research on marijuana's possible effects on the brain.
Marijuana and psychosisSlide 2 of 15
Marijuana and psychosis
Multiple studies have linked marijuana use with a higher risk of psychosis, which is a medical term that applies to symptoms that involve losing touch with the real world, such as hallucinations or paranoia. For example, in an analysis published in 2016 in the journal Schizophrenia Bulletin, researchers looked at previous studies of about 67,000 people.
They found that people in the study who used the most marijuana were more likely to be diagnosed with a psychotic mental-health condition, such as schizophrenia, than people who had never used marijuana.
A review published in April 2016 in the journal Biological Psychiatry also found a link between cannabis use and an increased risk of psychosis. "Overall, evidence from epidemiologic studies provides strong enough evidence to warrant a public health message that cannabis use can increase the risk of psychotic disorders," the authors wrote in the review.Slide 3 of 15
Pot and IQSlide 4 of 15
Pot and IQ
Teens who smoke pot may be more likely to experience an IQ drop when they are older, research has suggested. In a study of more than 1,000 people in New Zealand, researchers administered IQ tests to the participants twice: when they were 13, and then again when they were 38. The researchers also asked the participants about their drug use throughout the study period.
About 5 percent of the teens in the study had started using pot when they were teens. And it turned out that those who smoked pot at least four times a week and continued to use pot throughout their lives experienced an IQ drop of 8 points by the end of the study, on average. [6 Foods That Are Good For Your Brain]
It's not clear why pot may have negative effects on people's IQ, but it could be that teens are more vulnerable to pot's effects on brain chemistry, Susan Tapert, a neuropsychologist at the University of California, San Diego, who was not involved in the study, told Live Science in a 2012 interview.Slide 5 of 15
Brain size, connectivitySlide 6 of 15
Brain size, connectivity
Using marijuana for many years may be linked to changes in brain size, research has suggested. In a study published in November 2014 in the journal Proceedings of the National Academy of Sciences, researchers looked at 48 adults who used the drug at least three times a day, for an average of eight or nine years, and 62 people who didn't use marijuana. It turned out that the people who had been smoking pot daily for at least four years had a smaller volume of gray matter in a brain region called the orbitofrontal cortex, which previous research had linked to addiction. [3D Images: Exploring the Human Brain]
But the researchers also found that the brains of the chronic marijuana users showed greater connectivity, which is generally a measure of how well information travels between different parts of the brain.
The researchers said they don't know for sure why chronic marijuana use is linked to these brain changes, but they think it may have something to do with THC (tetrahydrocannabinol), marijuana's main psychoactive ingredient. This is because THC has been shown to affect cannabinoid receptors, which are involved in appetite, memory and mood, and are present in large numbers in the orbitofrontal cortex.Slide 7 of 15
The brain's reward systemSlide 8 of 15